There's a new kid in town and Hillary Clinton, to quote the Eagles, is likely saying "I don't want to hear any more."

Quinnipiac polling shows that support for Sen. Bernie Sanders (I-Vt.) among likely Democratic primary voters has ballooned from only 4 percent in March to 8 percent in April, and to 15 percent on May 28. Among "very liberal" Democrats, he draws 28 percent.

Clinton remains far ahead, but at 57 percent (down from 61 percent in April), she is nearing the 50 percent mark  the point at which a majority of Democratic primary voters do not want to vote for her.

And on the stump, Sanders is doing well. In Minneapolis on Sunday, he drew thousands and, according to The New York Times, got 240 people in Kensett, Iowa  population 256  to come to a community center on Saturday.

Hearing footsteps, the county Democratic chairman texted Troy Price, Clinton's Iowa political director, who replied "objects in the rear view mirror are closer than they appear."

The surest evidence that Sanders is closing in on the former secretary of State is that Mother Jones dug up  perhaps with help from her famous "secret police"  a 1972 essay he wrote called "Man  and Woman" that included rape fantasies echoing Fifty Shades of Gray. Chuck Todd even asked the senator about it on "Meet the Press."

The fact that Sanders is opening up space for himself and other challengers to Clinton is partially because his challenge is based not on her obvious ethical problems but on her questionable fealty to left-wing causes.

What are Democratic true believers to make of her encouragement of the Keystone oil pipeline and of the close contacts between Paul Elliott, a former Clinton aide and a top pro-pipeline lobbyist, and then-Clinton chief of staff Cheryl Mills, even as the State Department was preparing to approve the project? And what of the Democratic front-runner's refusal to oppose President Obama's Trans-Pacific trade treaty and of her past support for the North American Free Trade Agreement?

Sanders is determined to craft a genuine left-wing candidacy that urges higher taxes, single-payer healthcare and opposition to all free trade deals.

In primaries and particularly in caucuses, like Iowa, true believers predominate, and an ideological campaign against Clinton will attract a lot of support.

One can hammer on the former first lady as daily ethics conflicts emerge and her family's business dealings come close to outright bribery; leftist ideologues will put up with what they must to elect a compatriot president.

But when the ideological bent of their candidate is questioned, and the footprints of her husband's triangulation become evident in her own policy positions, they will grow restive indeed.

And when Sanders directly challenges her infidelity to liberalism in televised presidential debates, he will win adherents in droves.

The Vermont senator, for his part, only needs to get close. If he demonstrates that Clinton's candidacy has an element of vulnerability, he can smoke her out of hiding, and make her face the media and the country. There, she will have to answer tough questions that will only make things worse for her.

Once she is no longer the inevitable candidate, her ethical problems will begin to grate on Democratic primary voters, and her poll numbers will slip. Then, doubts about her ability to win in November will erode her standing further.

Will 1968 resurrect itself in 2016? Will the role of Eugene McCarthy that year now be played by Sanders, as he comes closer and closer to beating Clinton, allowing a more electable candidate to emerge? Will the role of Bobby Kennedy, who entered the race late to exploit the front-runner's vulnerability, be played by Massachusetts Sen. Elizabeth Warren? Will the Obama administration, thought by many to be behind the avalanche of exposés on Clinton, encourage a rival candidate?